A machine tool having a numerical control device performs machining while moving a movable unit by controlling each shaft such that a tool moves to a commanded position. In the machine tool having a rotary shaft, the rotary shaft rotates so as to change the posture of the tool relative to a workpiece. Therefore, machining may be performed on a sloping surface or a side surface of a workpiece.
In the machine tool having the rotary shaft, in a case of rotating the rotary shaft, due to the positional relation between the tool, a rotary table and a workpiece, the tool may interfere with the rotary table or the workpiece.
FIG. 2 is a schematic view illustrating an example of a machine tool having two rotary shafts provided to a rotary table. In FIG. 2, a rotary table of the machine tool to be an object of control has a rotary axis C for table rotation with respect to a Z axis and an inclined rotary axis A for tilting with respect to an X axis. Also, FIG. 6 is a view illustrating an example in which the tool interferes with the rotary table in a case of rotating the rotary axis A, and FIG. 7 is a view illustrating an example in which the tool interferes with a workpiece in a case of rotating the rotary axis C.
In the conventional numerical control device, in order to avoid interference of the tool with the rotary table or the workpiece, a worker manually evacuates the tool. Alternatively, a tool model representing a portion of the machine tool in a 3D shape is stored, and it is checked whether interference will occur. In a case of determining that interference will occur, the shaft operation stops immediately before the interference (see Patent Document 1, for instance).